Filter with cleaning by direct scavenging

ABSTRACT

The filter comprises a tubular body (1) provided with fixing flanges (2,3) for a fluid pipe. An upstream distributing plate (4) is perforated with orifices and extended by sockets (5) which are engaged in the up-stream ends of filtering elements (6). These elements (6) extend axially inside of the body (1). The filter comprises in its downstream part a collector (12) provided with bevelled tubes (13) which are engaged in the down-stream ends of the filtering elements (6). This collector (12) is continued by an elbow (11) which is followed by a single flush branching (7) opening laterally outside of the body (1).

FIELD OF THE INVENTION

The present invention relates to a filter intended to be mounted in afluid pipe, particularly in a pipe for untreated water, having adiameter substantially equal to that of the body of the filter.

BACKGROUND OF THE INVENTION

Generally speaking, automatic fast filters are provided with motorizedmechanical systems for ensuring their cleaning and are always cleaned byback wash.

These mechanical systems need a pluri-metallic construction, thuscorrosive, and the cleaning by back wash induces a risk of tackingand/or felting of the filtering elements when the water to be filteredcontains fibers.

Swiss patents Nos. 516.331, 532.409, 597.894 and 678.400 in the name ofthe applicant provide solutions to the above mentioned disadvantages asthey describe filters with cleaning by direct scavenging of thefiltering surface. Patents Nos. 516.331 and 532.409 disclose a simplemono-element filter with laminar cleaning on a tubular filteringelement, in which a current of untreated water is flushed at the momentof cleaning by opening of a flush valve normally closed. These twopatents also explain the evolution of a virtual filtration ringdeveloping from down-stream to up-stream according to the stage ofclogging of the filter. This theory allows to design a multielementfilter with several finenesses, described in patent No. 597.894 in whicheach filtering element is extended by a knee crossing through the bodyof the filter by a branching and a flushing valve, normally closed. Allthese individual flush branchings are then connected to a flushingcollector. These filters work perfectly, but they are expensive tomanufacture, because of the multiplication of the flush branchings andof the valves.

Patent 678.400 allows to lower the manufacturing cost of such filters byintroducing a turbo-distributor which brings into contact each filteringelement one after the other with one single flush outlet. This allows tohave only one flush branching and only one automatic valve (instead of 6or 8), to suppress the flushing collector and to simplify theinstallation and the programming of such a filter. Nevertheless thelatter presents the following disadvantages:

The rotor of the turbo-distributor is an expensive part relativelycomplex to manufacture. In the presence of untreated water charged withimpurities, one observes a wear of the moveable parts, such as the rotorof the turbo distributor. In certain extreme conditions, the rotor maygrip, which needs a disassembling of the filter and thus the temporaryclosure of the water pipe of the filter.

SUMMARY OF THE INVENTION

The multi-element filter according to the present invention withcleaning by direct scavenging intended to be mounted in a fluid pipeallows to prevent the abovementioned disadvantages and is characterizedby the features defined in claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The attached drawing illustrates schematically and by way of an examplean embodiment of the filter according to the present invention.

FIG. 1 represents a longitudinal section of the filter according to theinvention.

FIG. 2 is a cross-section according to line I--I of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The filter illustrated in FIG. 1 comprises a tubular body 1 with adiameter which is substantially equal to that of the pipe in which ithas to be mounted. The body 1 is provided at both of its ends withflanges 2,3 allowing to fix it to the said pipe. The up-stream end ofthe body 1 is provided with a distributing plate 4 in contact withflange 2, perforated with orifices and affixed to body 1 of the filterby screws (not shown). This plate 4 comprises sockets 5 emerging insideof the body and feeding the tubular filtering elements 6 which extendaxially inside of the body 1. The upstream end of said elements isengaged on one of said sockets 5.

The body 1 comprises on its down-stream part a single flush branching 7connecting the inside of body 1 to the outside. This flush branching 7,in the form of a tube of small diameter, is provided with a flange 8allowing to connect it to a flushing valve (not shown), preferablyautomatic, which normally is closed. The flush branching 7 is providedwith a branching 9 of small diameter, which permits its connection to ameasuring device for the upstream pressure. On its down-stream part thebody 1 is also provided with a branching of small diameter 10 allowingto connect thereon a measuring device for the downstream pressure of thefilter. These two pressure measuring devices permit to know the pressuredrop (untreated water/filtered water) of the filter.

The flush branching 7 is connected inside of the body I by means of anelbow 11 to a chamber 12 having the function of a collector whosegeneral form is that of a rotational solid. The form of this chamber inthe embodiment shown is conical widening out towards the up-stream endof the filter. The up-stream end proper of this collector is cylindricaland its front wall is preferably convex, generally in the form of aportion of a sphere. Said front wall may also be flat.

Bevelled tubes 13 of a diameter corresponding to the sockets 5 integralwith the distributing plate 4 and aligned with these sockets are affixedto the front wall through which they cross starting from the up-streampart of the chamber forming the collector 12. These tubes engage withthe down-stream end of the filtering elements 6.

The fact that the tubes 13 are bevelled facilitates the mounting of thefiltering elements and allows to avoid to bevel the up-stream end ofthese tubes 13.

This construction allows to provide a central filtering element 6,located on the axis of the filter and not only a ring of filteringelements as in the rotor monobranching filters. The filtration capacityof the filter is thus increased for the same diameter and the samelength of the latter.

When fitted in the pipe of fluid to be filtered by means of the flanges2,3, the filter works in the following manner:

In the case of water filtration, the water to be filtered enters with aspeed generally comprised between 2 and 15 m/s across the up-streamdistributing plate 4 in the filtering elements 6 and flows out througheach of these elements on their down-stream end in the form of a narrowvirtual ring which constitutes the filtering zone of the element. Bypassing through the filtering elements, the untreated water deposits itsimpurities which form a tight sleeve displacing the virtual filtrationring from down-stream to up-stream. The water thus filtered flows in theannular space located between the tubular body of the filter and thecollector 12 towards the down-stream outlet of the filter.

Progressively during its use, the annular zones of filtration risetowards the up-stream part of the filter and finally clog up the latter.It results in an increase of the pressure drop detected by the pressuremeasuring devices which automatically start a washing cycle of thefilter. Practically it is preferable to start this washing cycle of thefilter before the clogging, for example by means of a programmed timer,in order to avoid a pressure drop in the pipe.

The washing cycle lasting about 10 to 25 seconds is initiated by openingof the flush valve (not shown) located at the end of the flush branching7. This flush branching 7, connected by means an elbow 11 to chamber 12,drains all the filtering elements 6 simultaneously at one and the sametime. The truncated conical form of chamber 12, getting narrower towardsthe down-stream part of the filter, increases the flushing effect bycreating a whirling movement. It should be observed that a cylindricalnon-conical collector may also give an acceptable efficiency.

During the periodical flushing, the flush flow ranges at about 30% ofthe nominal flush; it follows during the flushing an increase of thetotal flow absorbed by the filter. This increase is generally assuredwithout trouble by the hydraulic circuit. If the filter functions at anominal speed of 7.5 m/s in the filtering elements, the increase of theflow caused by the flushing modifies the speed to approximately 10 m/s,thus guaranteeing a perfect cleaning of the filtering elements by directscavenging.

This short periodical flushing allows extremely low consumption ofuntreated washing water; practice shows that this consumption is lowerthan one percent in normal filtration. The filter remains functionaleven for lower nominal speeds in the range of 5-6 m/s. As a matter offact even in these cases a scavenging speed in the range of 6.5 m/s isobtained during the flushing of the filter which is sufficient.

In extreme cases, as in presence of heavily charged water and if thefilter is clogged, it is possible to close the output valve of thefilter during the flushing; this causes the differential pressure whichpresses the impurities against the filtering elements to be reduced tozero and allows the evacuation of said impurities by direct scavengingduring the flushing. The duration of the flushing being very short, inthe range of some tens of seconds, the temporary interruption of thehydraulic circuit is of no consequence.

It should be observed, that an elementary filter constituted by only onefiltering element continued by a flushing valve of the same diameter asthe element leads to a flushing flow which is incompatible with thepossibilities of the pipe net. It is therefore necessary to reduce theflushing circuit. Experience shows that in these conditions the activevein (which presents a sufficient speed) has substantially the samediameter as the reduced flushing orifice and, around this axial columnof water, a zone of lower speed travels through the surface of thefiltering element without cleaning it. The advantage of a multi-elementwith single flushing is to avoid this disadvantage; one obtains indeed asufficient filtering surface, a flushing of a reduced section compatiblewith the possibilites of the pipe net and the flow of the filteringelements is not unitarily reduced; the scavenging speeds are thushighest along the filtering surfaces allowing perfect cleaning.

The advantage of such a filter can be resumed as follows:

A multi-element filter, eventually with variable fineness, allowing toclean the elements by direct scavenging during short periodicalflushings which clean the whole filtering elements at one and the sametime without causing an important pressure drop.

This filter does not include any mobile part liable to wear in heavyworking conditions (water heavily charged with impurities). The filteris thus entirely static and its manufacturing costs are about twicelower than the known filters, while guaranteeing the same efficiency, asit is easy to manufacture and to assemble in great series.

In a variant, it is possible to provide deflector means inside thecollector 12, for example blades, causing a whirling flow of the waterduring the flushing of the filter. Such a whirling flow improves theflush action and the cleaning of the filter by increasing the flow speedof the water and by creating hydraulic vibrations in this flow.

The fact to provide a central filtering element 6, located on the axisof the filter, allows also to create a whirling flow during the flushingof the filter, while it increases the nominal flow of the filter ofequal size.

The filter according to the present invention is the optimum realisationfor a filter of this type; it combines a very great reliability (nomobile part) with a very low price, its elements being easy tomanufacture and to assemble, whilst ensuring a fast filtration in therange of 50 to 1000 microns, preferably of 100 to 500 microns.

I claim:
 1. In a filter with cleaning by direct scavenging intended tobe mounted in a fluid pipe, comprising: a tubular body of a diametersubstantially equal to that of the pipe, an up-stream distributing platecomprising a plurality of orifices feeding each an end of a tubularfiltering element extending axially inside of the body, the improvementwherein the down-stream end of all filtering elements are permanentlyand directly connected to a same and single flushing branching openinglaterally outside of the body and intended to be equipped with a valve.2. A filter as claimed in claim 1, wherein the filtering elements areconnected to said flushing branching by means of a frusto conicalchamber (12) and an elbow (11).
 3. A filter according to claim 2,wherein the frusto conical chamber has a truncated conical form wideningout towards the up-stream part of the filter.
 4. A filter according toclaim 3, wherein the up-stream part of the frusto conical chamberpresents a cylindrical portion.
 5. A filter according to claim 3,wherein the up-stream face of the chamber is convex.
 6. A filter asclaimed in claim 2, further including a series of first filteringelements disposed along a circumference and at least one secondfiltering element disposed centrally of said other filtering elements.7. A filter as claimed in claim 6, wherein only one second filteringelement is provided, located concentrically to the body of the filter.8. A filter according to claim 2, wherein the base of the chambercomprises bevelled tubes intended to engage with the down-stream end ofthe filtering elements, whilst the upstream end of each of the filteringelements is engaged with sockets integral with the distributing plate.9. A filter according to claim 2, wherein the chamber comprises meanscreating during the flushing a whirling flow and/or hydraulic vibrationsin the flow.
 10. A filter according to claim 1, wherein the filtrationfineness of the filtering elements is comprised between 50 and 1000microns.
 11. A filter according to claim 10, wherein the filtrationfineness of the filtering elements is comprised between 100 and 500microns.
 12. A filter according to claim 1, wherein said filter isconstituted exclusively by static parts.
 13. A filter according to claim1, further including a series of filtering elements arranged in a ringand a central filtering element located on the axis of the filter.